The present invention is related to railway tank cars and in particular to a protective structure for the various valves ordinarily present on the top of a cargo tank of such a railway tank car.
Nozzles have long been provided on the top of a railway tank car as manways and as locations for mounting groups of valves, including those used to fill a cargo tank with a fluid cargo, to remove the fluid cargo from the cargo tank, and to protect against excessive internal pressure. It has long been recognized that the nozzles are susceptible to being broken loose from the tank and that the valves can be broken in the event of a rollover of a railway tank car. Various housings have been used in the past to protect the valves, but they have been attached to a nozzle or a valve-mounting plate fastened to a nozzle. Various strengthened and reinforced nozzle structures have been provided in order to resist breakage of the nozzles in the case of a rollover, but previously known protective structures have failed when tank cars have overturned while moving along a railway.
Railway industry regulations require structures intended to protect tank top fittings on railway tank cars to be able to withstand longitudinally-applied forces equal to the weight of the cargo tank and its lading, and to be able to withstand laterally-applied forces of half that magnitude well enough to prevent failure of the fittings protected by such structures.
At least until recently, it had been considered unnecessary and an undesirable addition of weight to a railroad tank car to provide a strong protective structure surrounding a manway nozzle or a valve group nozzle on the top of a railroad tank car. Instead, welded gussets and various arrangements of strengthening of the attachment of a nozzle to the top of a cargo tank had been used in the past, as well as protective bells that can be attached to the valve group mounting plate to surround the valves and protect the valves themselves from damage in collisions and overturning. While previously available protection for the top of a tank car has value, various events have recently proven that protection to be insufficient in the case of overturning of railroad tank cars in motion along a railroad track.
What is needed, then, is a substantial yet not overly massive structure for protecting the various valves on the top of a cargo tank of a railway tank car, to prevent loss of cargo, and particularly to prevent escape of dangerous gaseous cargo or flammable liquid cargo, in the event of derailment and overturning of a moving railway tank car. Such a protective structure should not be so heavy as to add significantly to the fuel requirements for moving the car along the railway, yet it should be of ample strength. It is desirable also to have a protective structure on the top of a cargo tank be no larger than necessary, in order that it be a smaller target which can collide with an obstruction on the ground in the case of a rollover.
In a railway tank car that includes one embodiment of the invention disclosed herein, a substantial mounting, or bolting, flange is mounted in a first opening in the top of the cargo tank at a position lower than the position of a bolting flange for receiving a mounting plate for groups of valves and related fittings in a traditional nozzle.
In one embodiment of the structure disclosed herein for the top of a cargo tank of a railway car, a protective housing of plate metal extends upward from the top of the cargo tank and surrounds the nozzle for a valve group bolting flange and a mounting plate bolted to the flange, extending upward at least to the height of the highest valve or other fitting mounted on the valve group mounting plate.
In one embodiment of the structure of the top of a cargo tank for a railway tank car as disclosed herein, a pressure relief safety valve is mounted on a flange carried on a nozzle located at a second opening through the tank top, spaced a small distance apart from the valve group and fittings nozzle, and an auxiliary protective housing of metal plate construction extends around the nozzle and flange and has a pair of parallel side portions extending to and attached to the protective housing surrounding the valve group nozzle and its bolting flange. The auxiliary housing also acts as a bolster to help support the protective housing surrounding the valve group mounting plate.
In one embodiment, the auxiliary protective housing surrounding the pressure relief safety valve nozzle may be upwardly open to provide a path for fluids escaping through the pressure relief valve.
A railway tank car that includes one embodiment of the tank top protective structure disclosed herein includes a tank top reinforcement in the form of a doubler plate attached to the outer surface of the tank top, such as by welding, and a protective structure configured to the tank top and including an upstanding wall of metal plate is welded to the reinforcement doubler plate and is located radially outwardly spaced apart from the mounting flange of the valve group nozzle, so as to protect fittings mounted the nozzle.
Such a protective structure in one embodiment of the railway tank car disclosed herein includes a reinforcing band located on an upper portion of the upstanding wall to strengthen the reinforcing structure in the areas most likely to be subjected to external forces in the event of a rollover, yet avoid adding weight unnecessarily to the tank car.
The protective structure disclosed herein may be efficiently added to a conventional railway tank car to make such a car significantly less vulnerable to catastrophic damage and loss of fluid cargo in the event of a rollover.
The foregoing and other objectives and features of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.